Make a series of line drawings of polyhedral models
to show how all of the possible junction labellings given in
Fig. 44 may arise in practice.

Making the assumptions given in the Section on line labelling,
how many different junction types are potentially possible? What
fraction of these do the permissible labellings correspond to?

Draw a rectangular arch to show
how T-junctions can arise when part of an object obscures
another part of itself.

Amend the line labelling descriptions to take into
account shadow information. How many different junction types are
potentially possible? What fraction of these do the permissible
labellings correspond to? Compare your answer to that of
Exercise 2.

Design a relaxation labelling algorithm to implement the line
labelling method discussed.

Design a constraint satisfaction algorithm to implement the line
labelling method discussed.

Show how your algorithm works by tracing through a labelling example.

Give an example of an ambiguous figure for which the line labelling
algorithm would not find a unique label.

Label the following figures (fig 46) according the the line
labelling scheme: